MDEV-30415 PERIOD false positive overlap wtih utf8mb4_unicode_nopad_ci

A wrong UNIQUE violation is caused here by camparing strings
'def' and 'def ' (with space), under utf8mb4_unicode_nopad_ci collation,
which means "don't count in paddings when comparing".

Field::cmp_prefix uses a comparison through collation, so cmp_binary should
be used instead.

mysql-test/suite/period/r/overlaps.result

@@ -351,3 +351,18 @@ primary key(id, p without overlaps)
 ) engine=heap partition by hash(id);
 update t set id = 1;
 drop table t, t1;
+# MDEV-30415 PERIOD false positive overlap wtih utf8mb4_unicode_nopad_ci
+create table `t1` (
+datetime_column_name_1 datetime(6) not null,
+datetime_column_name_2 datetime(6) not null,
+text_column_name text collate utf8mb4_unicode_nopad_ci not null,
+period for p (datetime_column_name_1, datetime_column_name_2),
+unique key index_name (text_column_name(191), p without overlaps)
+) engine=innodb default charset=utf8mb4 collate=utf8mb4_unicode_nopad_ci;
+insert into t1 values ('2000-01-01', '2001-01-01', 'def '),
+('2000-01-01', '2001-01-01', 'def');
+truncate t1;
+insert into t1 values ('2000-01-01', '2001-01-01', 'def'),
+('2000-01-01', '2001-01-01', 'def '),
+('2000-01-01', '2001-01-01', 'def  ');
+drop table t1;

mysql-test/suite/period/t/overlaps.test

@@ -344,3 +344,23 @@ create or replace table t (id int, s date, e date, period for p(s,e),
 update t set id = 1;
 
 drop table t, t1;
+
+
+--echo # MDEV-30415 PERIOD false positive overlap wtih utf8mb4_unicode_nopad_ci
+
+create table `t1` (
+  datetime_column_name_1 datetime(6) not null,
+  datetime_column_name_2 datetime(6) not null,
+  text_column_name text collate utf8mb4_unicode_nopad_ci not null,
+  period for p (datetime_column_name_1, datetime_column_name_2),
+  unique key index_name (text_column_name(191), p without overlaps)
+) engine=innodb default charset=utf8mb4 collate=utf8mb4_unicode_nopad_ci;
+
+
+insert into t1 values ('2000-01-01', '2001-01-01', 'def '),
+                      ('2000-01-01', '2001-01-01', 'def');
+truncate t1;
+insert into t1 values ('2000-01-01', '2001-01-01', 'def'),
+                      ('2000-01-01', '2001-01-01', 'def '),
+                      ('2000-01-01', '2001-01-01', 'def  ');
+drop table t1;

sql/table.cc

@@ -9025,7 +9025,7 @@ bool TABLE::check_period_overlaps(const KEY &key,
       if (f->is_null_in_record(lhs) || f->is_null_in_record(rhs))
         return false;
     uint kp_len= key.key_part[part_nr].length;
-    if (f->cmp_prefix(f->ptr_in_record(lhs), f->ptr_in_record(rhs),
+    if (f->cmp_binary(f->ptr_in_record(lhs), f->ptr_in_record(rhs),
                       kp_len) != 0)
       return false;
   }